From the 1948 discovery of the apical ectodermal ridge in proximal-distal limb development to FGF molecular signals

This article, and indeed the foundation for much of the study of limb development, starts from the observations by then graduate student John Saunders. In 1948, Dr. Saunders published his thesis work "The proximo-distal sequence of origin of the parts of the chick wing and the role of the ectoderm". These pioneering studies showed that the apical ectodermal ridge or AER is required for outgrowth and patterning of the chick limb. This mini-review highlights Dr. Saunders' work and subsequent investigations to uncover the molecular mechanisms underlying proximal-distal development of the vertebrate limb.